The invention relates to a plant for producing pallet-less stacks of piece goods, particularly sacks around which is shrunk a sheet, with free spaces formed in the vicinity of the stack base for inserting conveying and lifting mechanisms, such as the arms of the fork of a fork lift truck or the like, using a stacking conveyor belt.
Methods and apparatuses for producing protective packings of shrunk plastics film or sheeting for load units of a plurality of superimposed layers of piece goods or bundles and a bottom bundle layer, which acts as an auxiliary pallet, with a smaller base surface than that of the superimposed layers of bundles, whilst forming free spaces located laterally of the auxiliary pallet for the engagement of the fork arms of fork lift trucks during the transportation of the load units are known in various forms.
Thus, from DOS No. 2,303,128, published Aug. 1, 1974 a bundle is known comprising a plurality of layers of superimposed packing articles which is surrounded by a plastics sheet, where the lowermost layer bends at a considerable distance from the lateral edges of the layers placed thereon, so that as a result two elongated spaces are formed for receiving the forked members of a fork lift truck. The plastics sheet extends into these spaces in such a way that it completely surrounds the faces thereof turned outwards and downwards. The lowermost layer of the packing articles is separately wrapped in a plastics sheet, whilst a further plastics sheet for covering the upper layers is welded or heat sealed at least along two parallel longitudinal sides to the plastics sheet covering the lower layer. Such a load unit comprising a plurality of superimposed bundle layers is provided with an auxiliary pallet formed from a bundle layer with a smaller bearing surface than the base surface of the actual stack. This bundle layer acting as an auxiliary pallet is separately wrapped prior to the wrapping of the entire stack with sheeting. The edges of the sheeting are welded, so that a water-tight wrapping for the auxiliary pallet is obtained. The individual bundle layers stacked on an auxiliary pallet formed in this way are then combined as a stack, wrapped by means of a vertical sheet banderole having in the upper area a projecting sheeting length, welded together at the facing edges, whilst the tips which are thereby formed are simultaneously engaged on the top of the stack. The actual load units can be produced in such a way that the auxiliary pallet comprising a bundle layer is placed on the top of the stack formed and the latter is placed on a sheet subsequently forming the upper cover of the protective pack. The stack is then wrapped in sheeting and at the same time the sheeting is guided in the vicinity of the recesses formed by the auxiliary pallet with respect to the underlying bundle layer for engaging the fork arms of fork lift trucks during the transportation of the load units. The sheet wrapping placed over the stack is then edge-welded to the cover sheet and, at the end of the sheet shrinkage process, the complete load unit is turned by 180.degree., so that the initially uppermost auxiliary pallet forms the base surface for the stack. However, in this known construction it is disadvantageous that the most stressed points of the protective pack are only constructed in single-layer form and that there is no accurate formation of the recesses for inserting the fork arms of fork lift consequently damage can, in particular, occur in this sheeting area in which the fork arms of the fork lift trucks are inserted below the load laterally of the auxiliary pallet.
The use of partly sheet-wrapped pallets for producing load units is also known from U.S. Pat. No. 3,640,048. According to this patent, such a load unit is produced in that a sheet blank with an all-round sheet projection is placed on the unloaded pallet. Successive bundle layers are then placed on the thus prepared pallet to form a stack. Before or after fitting a vertical sheet banderole to the stack, a cover sheet is placed on the uppermost bundle layer and the vertical sheet banderole, the cover sheet and the lower sheet blank are welded and shrunk around the pallet load.
In addition, a method is known, from DAS No. 2,614,558 published Aug. 28, 1980 (corresponding in part to U.S. Pat. No. 4,060,957 issued Dec. 6, 1977) for producing a packing unit, which is completely wrapped in a shrink sheet or film, has no pallets and comprises a plurality of layers of stacked articles. Initially, several layers of articles with the same base area are stacked one upon the other. Then a special layer of articles is stacked in such a way that at least two parallel recesses are formed at right angles to the stack conveying direction for the subsequent engagement of the supporting members of a lifting appliance. A first dome-shaped covering of shrink sheeting is drawn from above over the complete stack and is then shrunk closely onto the latter by heat application. The complete stack is then turned by 180.degree. in such a way that the special layer with the recesses is located at the bottom. However, this leads to the advantage that the sheet-wrapped stack can only be removed at right angles to the longitudinal direction of the conveyor belt, because the recesses are also transversely directed on either side of the special layer. In this known method, prior to stacking the special layer, an additional plastic sheet is placed on the stack, whose edges which are parallel to the recesses hang down somewhat laterally of the stack. After turning the stack by 180.degree., a second dome-shaped shrink sheeting is drawn over the stack and is closely shrunk thereon by heat application in such a way that the areas of the additional plastics sheet positioned laterally of the stack form three-layer overlapping areas for the lateral areas of the first covering and lateral areas of the second covering.
The high consumption of shrink sheeting for the two dome-shaped sheet coverings drawn over the stack is a disadvantage of this known method. As the coverings are formed from a correspondingly folded sheet web and it is necessary to separate the necessary covering length from said web, the upper and lower areas of the coverings drawn over the stack have, in each case, a weld located inter alia on the upper surface of the sheet wrapping. This is disadvantageous with regard to the sealing action, because such welds can easily be damaged and also are detrimental to the strength of the wrapping sheet. It is also disadvantageous that the sheet-wrapped stack is not supported after leaving the rotating mechanism in the vicinity of its two free spaces adjacent to the layer forming the base surface of the stack. Due to the lack of such a support the stack obtained does not have an adequate strength and in addition the projecting portions of the layer resting on the auxiliary pallet hang down into the free space area, so that often there is not enough space for inserting the fork of a fork lift truck. The further heating of the complete sheet wrapping for shrinking the applied second sheet covering reduces the strength of the complete sheet wrapping, because it has been found that if a wrapping sheet is heated a number of times its strength is reduced.